1. Field of the Invention
The invention relates to a method, to a device, and to an assembly or system for reducing aerodynamic drag and mitigating detrimental effects of side wind on vehicles moving through air or water including but not limited to heavy cargo trucks, cargo containers, liquid cargo cisterns, buses, RV's, SUV's, vans, passenger cars, railroad cars, helicopters, airplanes, aerostats, ships and submarines, and, more specifically, to systems for introducing intensive small-scale turbulent vortices with large lifespan and/or sheets of small-scale-vortices into the vehicle's drag producing volumes. The invention also relates to attachable/detachable mounting of any devices on vehicles.
2. Description of the Related Art
In the context of the present invention, a vehicle is defined as any means for transporting people and/or cargo. The below description is focused on a specific application of the present invention to ground heavy cargo vehicles which is done for simplifying explanation of physical effects and major features of the invention. The description is as comprehensive as any person skilled in the art can apply the invention to any other vehicle that moves through air or water. The term aerodynamic drag, therefore, is to be understood to also refer to any fluid-dynamic drag.
With an increasing fuel cost, reducing fuel consumption by long distance cargo transport and other vehicles at a cruise speed became an increasingly important task and a diverse body of designs has been developed for reducing an aerodynamic drag of vehicles, mainly for large cargo trucks. Although the majority of efforts have been focused on reducing a vehicle drag for the cases of no wind or a head wind, a limited attention was also paid to reducing detrimental effects of side winds. The most important side wind effects include the increase in an aerodynamic drag of a vehicle at stable or gusty side winds and forcing a vehicle out of a traffic lane or overturning a vehicle by strong side wind gusts. Hereafter a side wind is defined as airflow around a vehicle at a non-zero yaw angle.
A standard cargo vehicle consists of a tractor and one or several cargo holding areas (containers) of any kind that are attached to a tractor or towed, referred below as trailers. As such vehicle moves along its path, airflow around the vehicle produces the aerodynamic drag and increases the fuel consumption. The major air drag-producing volumes are located in the front of a vehicle, on the sides of a vehicle, underneath a vehicle, in the gaps between a tractor and a trailer and between sequential trailers for combination vehicles, and on the back of trailers. The magnitude of aerodynamic drag increases significantly with increasing vehicle speed.
Modern trailers have a traditional parallelepiped shape with bluff edges for maximizing a cargo space. The front of modern tractors is typically of an aerodynamically efficient shape although the rear edges still have a bluff shape. Bluff rear edges are also typical for buses, RV's, railroad cars and some passenger SUV's, vans and cars. High air drag of bluff bodies compared to that of smooth bodies (also called aerodynamic bodies) is a well-known physical phenomenon.
The term “air drag” refers to the aerodynamic force acting on a vehicle and opposing its motion through the surrounding air. In general, such drag forces include friction drag (also called viscous drag) and pressure drag (also called form drag or profile drag). The physical basis for high air drag of bluff bodies at a high air speed is well-known. Due to the inertia, airflow around a bluff body cannot make a sharp turn and fill the space on the sides and behind a fast moving body, such as a tractor or trailer. It leads to flow separation on the bluff edges and creates a low pressure zone behind a bluff body and a pressure drop on its rear surface. Flow separation in front of a bluff body like a tractor windshield or a trailer front creates a high pressure zone and a pressure jump on its front surface. The difference in pressure between the rear surfaces and the respective front surfaces of a body creates the aerodynamic force acting against the body motion through surrounding air and this force is called the aerodynamic drag or air drag.
Air drag can be reduced by enhancing injection of air into a low pressure zone and/or by reducing a size of a separation zone. In accordance with Bernoulli's effect, a pressure drop on the rear surface and a pressure jump on the front surface of a bluff body decrease with decreasing the size of a respective flow separation zone.
A diverse body of devices has been developed for reducing air drag in drag-producing volumes in front and underneath motor vehicles, in the gaps between a tractor and a trailer and between sequential trailers for combination vehicles, on the sides of a trailer, and on the back of the trailers. Literally hundreds of patents for such devices have been awarded around the world for the last several decades. To enhance the efficiency of the previously invented devices, an application of several different drag-reducing devices in different location of the same vehicle has been suggested in many patents. The authors of the present invention do not intend to provide a comprehensive overview of all relevant patents but refer to typical examples of different drag-reducing devices for motor vehicles.
The majority of devices for reducing air drag for cargo vehicles are aimed at reducing the size of a flow separation zone and/or the pressure drop and/or the pressure jump inside the zone by streamlining airflow near bluff edges.
Modern tractors have aerodynamically efficient front profiles, high roof fairings and side cab extender fairings, for example U.S. Pat. No. 4,750,772 to Haegert, U.S. Pat. No. 4,932,716 to Marlowe et al., and references therein. Those means streamline airflow around a tractor body and reduce significantly its air drag.
The most widely used devices for streamlining airflow underneath cargo vehicles are aerodynamic skirts. Typical skirt configurations can be found, for example in U.S. Pat. No. 7,578,541 to Layfield et al., U.S. Pat. No. 7,740,303 to Wood, and references therein. Aerodynamic skirts streamline airflow around the drag-producing volume underneath a vehicle and reduce the vehicle's air drag.
Nose cones, front fairings and front deflectors are typically used for streamlining airflow around the trailer front; e.g., U.S. Pat. No. 5,280,990 to Rinard, the Patent application publication No. US 2008/0061598 by Reiman and Heppel, and references therein. Those devices reduce air drag in the gap between a tractor and a trailer and on the trailer roof and sides.
Another device for reducing air drag in the tractor-trailer gap are split plates, e.g., U.S. Pat. No. 6,986,544 to Wood, U.S. Pat. No. 7,318,620 to Wood and references therein. Instead of streamlining airflow, the plates split large turbulent vortices in the gap into several smaller ones which results in the drag reduction.
The largest fraction of the vehicle's air drag is concentrated in the trailer back and the majority of existing drag-reducing devices are focused on that drag-producing volume. The mostly used devices for reducing air drag in the trailer back are rear fairings, deflectors, boat tails, vanes and scoops. Representative examples of such devices can be found in U.S. Pat. No. 6,286,894 to Kingham, U.S. Pat. No. 6,309,010 to Whitten, U.S. Pat. No. 6,485,087 to Roberge et al., U.S. Pat. No. 6,595,578 to Calsoyds et al., U.S. Pat. No. 7,192,077 to Hilleman, U.S. Pat. No. 7,240,958 to Skopic, U.S. Pat. No. 7,243,980 to Vala, U.S. Pat. No. 7,585,015 to Wood, U.S. Pat. No. 7,641,262 to Nusbaum, U.S. Pat. No. 8,079,634 to Visser et al., the U.S. Publ. No. 2003/005913 by Leonard, and references in those patents. The rear fairings, deflectors, boat tails, vanes and scoops streamline airflow around rear bluff edges of motor vehicles and/or re-direct part of airflow around a trailer into a flow path close to the trailer's rear vertical surface which results in the decreased size of a low pressure zone behind the vehicle and/or the lower pressure drop and thus reduces the air drag.
Rear spoilers are also used for streamlining airflow around the rear bluff edges of motor vehicles; e.g., U.S. Pat. No. 4,863,213 to Deaver et al. and references therein.
Another approach to reducing air drag in the back of motor vehicles is direct pumping of air into the trailer back; e.g., U.S. Pat. No. 6,561,575 to Fairburn et al., U.S. Pat. No. 6,685,256 to Shermer, U.S. Pat. No. 7,216,923 to Wong et al., and references in those patents. The air is taken from airflow around a vehicle or from a vehicle engine and delivered to the trailer back through air ducts.
Air deflectors on the trailer side walls were proposed for mitigating some of the detrimental effects of side winds; e.g., U.S. Pat. No. 6,224,141 to Brodlo, and references therein. The side deflectors of that patent streamline airflow around bluff edges on the sides of a trailer roof and prevent the trailer from overturning by strong side wind gusts.
All the above listed devices have several significant drawbacks that hinder their practical implementation. The devices are large in size, heavyweight, inconvenient in use and may interfere with operating cargo vehicles like loading and unloading. The most significant drawback of those devices is their inefficiency at side winds. Numerous scientific studies have shown that neither nose cones, split plates nor front and rear fairings and deflectors reduce noticeably air drag of cargo vehicles at side winds.
Another type of drag-reducing devices are small-scale vortex generators (SSVG) also referred to as small-scale turbulence generators, small eddy generators or generators of small-scale turbulence. For more than 80 years SSVG have been successfully used for a diversity of practical applications ranging from controlling a boundary layer on airfoils to reducing air drag of cargo vehicles.
The most well-known application of SSVG is that for aircraft wings, see, for example, U.S. Pat. No. 4,655,419 to van der Hoeven, U.S. Pat. No. 5,058,837 to Wheeler, U.S. Pat. No. 6,427,948 to Campbell, U.S. Pat. No. 6,491,260 to Borchers et al., and references in those patents. SSVG are widely used for delaying flow separation on airfoils and the aerodynamic stalling at high angles of attack and hence increasing the lift force and reducing intensity of harmful large-scale wingtip vortices.
Developed for airfoils, SSVG with minor or no modifications have been applied for reducing air drag on motor vehicles, e.g., U.S. Pat. No. 6,959,958 to Basford, U.S. Pat. No. 6,979,049 to Ortega et al., U.S. Pat. No. 7,255,387 to Wood, U.S. Pat. No. 7,431,381 to Wood, U.S. Pat. No. D432,073 to Coyle, and references in those patents.
Another broad application of SSVG is for intensifying turbulent mixing in heat exchangers, combustion chambers, automotive engines, paper machines and the like. Typical examples can be found in U.S. Pat. No. 4,359,997 to Lyssy, U.S. Pat. No. 4,836,151 to Litjens et al., U.S. Pat. No. 4,962,642 to Kim, U.S. Pat. No. 5,803,602 to Eroglu et al., U.S. Pat. No. 6,099,692 to Weisshuhn et al., U.S. Pat. No. 6,158,412 to Kim, U.S. Pat. No. 6,349,761 to Liu et al., and references in those patents.
Some of SSVG for intensifying turbulent mixing have also been adapted to drag reduction of motor vehicles. For example, widely used in combustion chambers porous plates were proposed as auxiliary walls around a whole trailer or its parts, e.g., U.S. Pat. No. 6,286,892 to Bauer et al. and references therein. Controllable air modulators are a representative example of more sophisticated implementation of small-scale vortices for reducing the trailer side and back air drag, for example the Patent application publication No. US 2009/0146452 by Kjellgren et al. and references therein.
SSVG have also been used for reducing air drag of mobile bodies, e.g., U.S. Pat. No. 7,934,686 to Harman, and references therein.
Prior art SSVG for motor vehicles share a significant drawback that was established in numerous scientific studies, namely, low efficiency in reducing air drag. The low efficiency results from considerable differences in operational requirements for vehicles from those for airfoils, combustion chambers, automotive engines and other conventional applications of SSVG. The basic requirement for all conventional applications is the lowest own aerodynamic resistance of SSVG. Airfoils are low-drag aerodynamic bodies operating at the flight speed of hundreds kilometers per hour and air ducts in combustion chambers, automotive engines and the like are designed as aerodynamically efficient transporters to ensure the highest airflow rate through the ducts. At the same time, only small lifespan and low intensity of generated vortices are required by conventional applications. For example, SSVG on air wings are typically required the vortices with a lifespan of less than half of the wing chord. In practice that value typically does not exceed half a meter and is comparable to the size of applied SSVG. The required lifespan of small-scale vortices in combustion chambers, automotive engines, heat exchangers and the like is typically of the order of few centimeters. To satisfy these requirements, all existing SSVG are open-type devices. In taking the path of least resistance, free airflow tries to keep itself away from the resistant obstacles and thus runs mainly outside the vortex-producing elements. Such self-adaptation of airflow ensures the lowest aerodynamic resistance of the open-type SSVG in accordance with the major requirement for conventional applications although leads to the low intensity and lifespan of generated small-scale vortices.
Motor vehicles impose completely different requirements on SSVG and the basic ones are the highest possible intensity and lifespan. Typical size of drag-producing volumes of cargo vehicles at the highway speed is from 3 m to 10 m with a typical size of harmful large-scale vortices in the same range. To effectively reduce air drag, SSVG for motor vehicles must generate highly intensive small-scale vortices with a lifespan comparable to the size of a drag-producing volume. At the same time, own aerodynamic resistance of SSVG is of low significance for motor vehicles due to a low driving speed of typically below 130 km/h and a very high air drag in the drag-producing volumes on bluff edges of large tractors and trailers.
As noted above, all existing SSVG for motor vehicles are either directly reproduced or slightly modified SSVG for airfoils, automotive engines and other conventional applications. Being the open-type devices with low aerodynamic resistance, they are physically inappropriate for producing intensive small-scale vortices with sufficiently large lifespan. Existing SSVG for motor vehicles generate low-intensity small-scale vortices with a short lifespan which results in a low reduction in the size of a flow separation zone, slight weakening of harmful large-scale vortices and thus low reduction in air drag of motor vehicles.
In addition, the majority of existing devices for reducing aerodynamic drag and mitigating detrimental effects of side winds are mounted permanently on external surfaces of motor vehicles.
Therefore, existing devices for reducing aerodynamic drag for vehicles at a cruise speed have the following significant shortcomings that hinder their practical implementation:                The devices are unable to reduce aerodynamic drag of vehicles to any significant degree, and        the majority of the devices are designed for airflow along the travel direction and they have a low efficiency in reducing detrimental effects of side winds.        
Additional shortcomings of existing devices for reducing an air drag and mitigating detrimental effects of side winds for long distance cargo vehicles at typical highway speeds are as follows.                The devices may interfere with loading and unloading cargo vehicles including opening and closing the trailer doors and backing into loading docks.        The devices may extend significantly from the trailer surfaces and be easily damaged when a vehicle maneuvers on uneven roadsides and/or is backed into loading docks.        The devices are technologically complicated, inconvenient to use and non-durable.        The devices that are permanently mounted on a trailer do not address an issue of separate ownership, for example, a tractor may belong to an independent owners-operator and towed trailers may belong to a fleet-owning company.        Existing mounting systems for attaching/detaching items such as tarp, temporary signs and the like to external vehicle surfaces do not allow attaching/detaching the items to trailer roof and sides by one person.        
A need therefore exists for developing an innovative system that overcomes those shortcomings.